This invention relates to an ICP plasma etching apparatus for etching a substrate, methods of reducing contamination, and to protective structures for plasma etching apparatus of this kind.
Plasma etching is widely used to process a variety of substrates, such as semiconductor wafers. The plasma etching process may be a step process which forms part of a process sequence. For example, in the semiconductor industry it is well known to remove materials from a wafer surface by a sputter etch process prior to a subsequent metal deposition step. The sputter etch process is typically performed using an Argon plasma. The purpose is to ensure a high quality metal/metal interface resulting in a low contact resistance. The sputter etch step is typically conducted in a pre-clean module.
In operation, it is observed that prolonged etching can result in a build up of redeposited particulate material around the interior surfaces of the sputter etch chamber, such as the chamber lid and walls. This is a particular problem with the etching of organic materials such as polyimide (PI) and polybenzoxazole (PBO) which can lead to a build up or redeposition of carbonaceous material. This redeposited particulate material can accumulate to a point where the particles become loose and there is the potential for them to fall onto and contaminate the wafer.
A further problem is associated with wafers that contain substances which outgas heavily. Examples of such substances are organic passivation layers, adhesives, photoresists and spin-on materials. Again, PI and PBO are especially problematic. When these materials outgas, contaminants are released into the chamber which raises the pressure. This can cause significant problems in recovering acceptable vacuum levels in the chamber between the processing of successive wafers.
The conventional solution to these problems is to perform a maintenance procedure on a frequent basis. This ultimately results in the chamber being vented to atmosphere so that a mechanical clean can be carried out. This intervention has a significant cost and tool downtime. This is not desirable in a production environment. Instead, it would be desirable to reduce the frequency of the maintenance interventions. This would reduce cost whilst improving the uptime of the tool.
It is also known to periodically etch a metallic disc or a metallised wafer in order to extend the mean time between cleans of the chamber. The chamber typically comprises a ceramic or quartz sidewall through which RF energy is inductively coupled to form a plasma in the chamber. It is important that this portion of the chamber is protected against the formation of a continuous metal deposition. Otherwise, severe attenuation of the inductively coupled power can occur. The etching of the metallic disc or metallised wafer results in the etch material “pasting” any loose particulate material onto an interior surface of the chamber. This prevents the particulate material from falling onto the substrate. However, normal manufacturing must be interrupted to perform the etching of the metallic disc or metallised wafer. Therefore, these techniques are disruptive to normal manufacturing, which results in a loss of system throughput and an increased cost of ownership (COO).